Simplified measurement of borehole fluid resistivity

ABSTRACT

A well logging system that includes a tool which is deployed within the well. The tool has a housing in which imaging hardware is stored, and on which sensors are located, where the sensors detect and measure electrical signals that have been induced in the formation surrounding the well. A wiper system is also mounted on the housing for clearing mud and other debris from outer surfaces of the sensors.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present disclosure relates in general to a system for use in imaging a subterranean borehole. More specifically, the present disclosure relates to a downhole imaging system having sensors, and with wiping elements for clearing any detritus that accumulates on the sensors.

2. Description of Prior Art

Geological data concerning subterranean formations is often gathered with an imaging technique. The data obtained usually relates to formation resistivity, formation porosity and/or permeability, identification of formation strata and the like. Zones of entrained hydrocarbons and reservoir production capabilities can be determined using this data. Often, the imaging is obtained with a downhole logging tool, which is deployed into a well that extends into the subterranean formation. Example downhole tools for imaging include resistivity tools, nuclear magnetic resonance (NMR) devices, and acoustic sensors. Resistivity tools usually include electrodes on one portion of the tool that are energized to emit a current into the formation, which is measured with sensors on another part of the tool. NMR devices release radiation that scatters from the formation, which is analyzed for assessing formation details. Similar to radiation devices, acoustic devices analyze acoustic data that reflects from the formation. The effectiveness of downhole sensors can be reduced when drilling mud or other material forms deposits on the surfaces of these sensors.

SUMMARY OF THE INVENTION

Disclosed herein is an example of a tool for imaging in a subterranean wellbore, that in an embodiment includes a housing, a sensor coupled with the housing that is in selective electrical communication with a formation intersected by the wellbore, and a wiper system having a wiper blade for selectively clearing a foreign substance from a surface of the sensor. The wiper system may further have a wiper rod that selectively reciprocates in a direction substantially parallel with an axis of the housing, and wherein the wiper blade is mounted in a wiper arm that is transversely coupled to the wiper rod. In this example, the wiper system further includes a motor selectively moving the wiper blade across the surface of the sensor. The sensor can be a planar electrode set or circular electrode set. In another example, the wiper blade is helically shaped and rotatable about the housing, so that when fluid flows axially past the housing, the fluid exerts a rotational force onto the wiper blade thereby causing the wiper blade to wipe across the surface of the sensor along a circular path. In this embodiment, opposing ends of the wiper blade are coupled with supports that rotate in a plane transverse to an axis of the housing. A transducer for creating an electrical field in and adjacent the wellbore can be included with the tool.

Another example of a tool for imaging in a subterranean wellbore includes a housing, sensors coupled with the housing having a surface in communication with fluid in the wellbore, and a pliable wiper blade selectively moveable across the surface and in contact with the surface so that the blade removes matter from the wellbore that adheres to the surface. The wiper blade may include polyether-ether-ketone and may also optionally be attached to a wiper arm for holding the wiper blade. Optionally included is a wiper assembly for reciprocating the wiper blade along a path substantially parallel with an axis of the housing. In an example, further included is a frame with a helical shaped arm in which the wiper blade is mounted and members coupled on opposing ends of the arm that rotationally mount the frame to the housing and so that when a fluid in the wellbore flows past the frame, a rotational force rotates the helical shaped arm and causes the wiper blade to sweep across the surfaces of the sensors.

BRIEF DESCRIPTION OF DRAWINGS

Some of the features and benefits of the present invention having been stated, others will become apparent as the description proceeds when taken in conjunction with the accompanying drawings, in which:

FIG. 1 is side partial sectional view of an example of a logging tool in a wellbore in accordance with the present invention.

FIG. 2 is a perspective view of an example embodiment of a wiper assembly for cleaning a sensor for use with the logging tool of FIG. 1 and in accordance with the present invention.

FIG. 3 is a perspective view of an alternate embodiment of a wiper assembly for cleaning a sensor for use with the logging tool of FIG. 1 and in accordance with the present invention.

While the invention will be described in connection with the preferred embodiments, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF INVENTION

The method and system of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments are shown. The method and system of the present disclosure may be in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey its scope to those skilled in the art. Like numbers refer to like elements throughout.

It is to be further understood that the scope of the present disclosure is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation.

FIG. 1 is a side partial sectional view of a downhole tool 10 disposed in a wellbore 12, where the wellbore 12 intersects a subterranean formation 14. The downhole tool 10 is deployed on wireline 16, which is illustrated extending through a wellhead assembly 18 that is on the surface at the opening of the wellbore 12. Sensors 20 are provided with the downhole tool 10 that in one example are depicted as electrodes 22 mounted on the tool body 24. In an example, the sensors 20 sense current in the formation 14; which generate an electromagnetic field in the formation 14 represented by flux lines 26. Current is induced in the formation 14 by a transmitter 28 schematically shown provided with the downhole tool 10. Formation resistivity can be estimated based on an evaluation of the current sensed by the sensors 20.

FIG. 2 is a perspective and enlarged view of a portion of an alternate embodiment of the downhole tool 10A of FIG. 1. In this example a recess 30A is shown formed on a side of the tool body 24A, where button sensors 22A are set on a bottom of the recess 30A. An example of a wiper assembly 32A is shown that is coupled with the downhole tool 10A and for clearing debris 33A, such as mud, fluid, formation cuttings, or any other detritus that may accumulate and/or adhere to an outer surface of one or more of the sensors 22A. In the illustrated example the wiper assembly 32A includes a wiper arm 34A, which has an elongate side extending generally transverse with an axis A_(X) of the tool body 24A. A wiper blade 36A is mounted in the wiper arm 36A, where in one example the wiper blade 36A is formed from a pliable material that can remove the debris 33A without damaging the downhole tool 10A. Examples of wiper blade 36A material include elastomers, rubber, polymers, polyether ether ketone, combinations thereof, and the like. The wiper arm 34A and wiper blade 36A of FIG. 2 are strategically located adjacent the bottom surface of the recess 30A so that the debris 33A can be removed from the sensors 22A by moving the wiper arm 34A and wiper blade 36A across the surface of the sensors 22A. Further included with the wiper assembly 30A is a wiper rod 38A, which is an elongate member that extends generally parallel with the axis A_(X) and on which the wiper arm 34A and wiper blade 36A are attached. In the example of FIG. 2, ends of the wiper rod 38A insert into axial passages P₁, P₂ in the tool body 24A. Further illustrated in the example is that one of the ends of the wiper rod 38A couples with a motor 40A via a pinned connection 41A with an output shaft 42A of the motor 40A. In this embodiment, operation of the motor 40A, rotates the shaft 42A, that in turn reciprocates the wiper rod 38A. Axial reciprocation of the wiper rod 38A slides the wiper arm 34A and wiper blade 36A back and force across the bottom of the recess 30A to thereby clear debris 33A from the outer surfaces of the sensors 22A.

Referring now to FIG. 3, shown in perspective and enlarged view is an alternate embodiment of a portion of the downhole tool 10B of FIG. 1. In this example, the sensors 22B are electrode ring type sensors that extend a circumference of the tool body 24B and that are spaced axially apart from one another. Also shown is an example of a wiper assembly 30B that includes a pair of wiper arms 34B and wiper blades 36A. Here, each wiper arm 34B and wiper blade 36A are attached to one another with free edges of the wiper blades 36A in scraping contact with the outer surfaces of the sensors 22B. Optionally, a single wiper arm 34B and wiper blade 36A assembly could be employed. The wiper arm 34B and wiper blade 36A are helically shaped and extend axially along a length of the tool body 24B. In the illustrated example, the distal ends of each wiper arm 34B and wiper blade 36A assembly extend past opposing distal ends of the sensors 22B to ensure debris 33B is cleared from the sensors 22B. The opposing ends of the wiper blades 36A are mounted to struts 43B, which are elongate members oriented transverse to the axis A_(X) and whose mid portions are pinned to the tool body 24B. The struts 43B are rotatable about the tool body 24B, thereby allowing the wiper arms 34B and wiper blades 36A to rotate about the tool body 24B so that the wiper arms 34B can scrape debris 33B from the sensors 22B. An advantage of the helically shaped wiper arms 34B and wiper blades 36A is that when fluid flows over the tool body 24B, schematically illustrated by arrows F, a resultant force is exerted onto the wiper assembly 30B causing it to rotate as represented by curved arrow A. As noted above, rotating the wiper assembly 30B, and thus wiper arm 34B and wiper blade 36A, scrapes or otherwise removes debris 33B from the surfaces of the sensors 22B. Also provided in the example of FIG. 3 is an optional ring like collar 44B shown circumscribing the tool body 24B and coupled with a one of the struts 43B.

The present invention described herein, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While a presently preferred embodiment of the invention has been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of the present invention disclosed herein and the scope of the appended claims. 

What is claimed is:
 1. A tool for imaging in a subterranean wellbore comprising: a housing; a sensor coupled with the housing that is in selective electrical communication with a formation intersected by the wellbore; and a wiper system having a wiper blade for selectively clearing a foreign substance from a surface of the sensor.
 2. The tool of claim 1, wherein the wiper system further comprises a wiper rod that selectively reciprocates in a direction substantially parallel with an axis of the housing, and wherein the wiper blade is mounted in a wiper arm that is transversely coupled to the wiper rod.
 3. The tool of claim 2, wherein the wiper system further comprises a motor selectively moving the wiper blade across the surface of the sensor.
 4. The tool of claim 2, wherein the sensor comprises a planar electrode set.
 5. The tool of claim 1, wherein the wiper blade is helically shaped and rotatable about the housing, so that when fluid flows axially past the housing, the fluid exerts a rotational force onto the wiper blade thereby causing the wiper blade to wipe across the surface of the sensor along a circular path.
 6. The tool of claim 5, wherein opposing ends of the wiper blade are coupled with supports that rotate in a plane transverse to an axis of the housing.
 7. The tool of claim 5, wherein the sensor comprises a cylindrical electrode set.
 8. The tool of claim 1, further comprising a transducer for creating an electrical field in and adjacent the wellbore.
 9. A tool for imaging in a subterranean wellbore comprising: a housing; sensors coupled with the housing having a surface in communication with fluid in the wellbore; and a pliable wiper blade selectively moveable across the surface and in contact with the surface so that the blade removes matter from the wellbore that adheres to the surface.
 10. The tool of claim 9, wherein the wiper blade comprises polyether-ether-ketone.
 11. The tool of claim 9, further comprising a wiper arm for holding the wiper blade.
 12. The tool of claim 9, further comprising a wiper assembly for reciprocating the wiper blade along a path substantially parallel with an axis of the housing.
 13. The tool of claim 9, further comprising a frame with a helical shaped arm in which the wiper blade is mounted and members coupled on opposing ends of the arm that rotationally mount the frame to the housing and so that when a fluid in the wellbore flows past the frame, a rotational force rotates the helical shaped arm and causes the wiper blade to sweep across the surfaces of the sensors. 